Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Plasma is a state of matter similar to gas in which at least part of the particles are ionized. The presence of charged particles (e.g. positive ions and negative electrons) makes plasma electrically conductive. Plasma with a magnetic field strong enough to influence the motion of the charged particles is called magnetized plasma. A plasma torus is a self-sustained magnetized plasma shaped into a toroidal configuration (donut shape), with linked poloidal and toroidal (in some cases) closed magnetic field lines. Toroidal magnetic field comprises magnetic field lines that go parallel to a magnetic axis of the plasma torus. The toroidal field is generated by a current flowing in poloidal direction around the plasma's magnetic axis. Poloidal magnetic field comprises magnetic field lines that go around the magnetic axis of the plasma torus and is generated by a current flowing in toroidal direction, parallel to the magnetic axis. As a magnetic field line runs many turns around the plasma in the toroidal and poloidal direction, it defines a “flux surface” at a constant radius from the plasma's magnetic axis. The extent of linkage of the poloidal and toroidal magnetic fluxes defines a helicity of the plasma torus. Plasma torus contained in a simply connected volume is called a compact toroid (CT). The CT configuration can include, for example: a spheromak configuration that exists close to a stable magnetohydrodynamic equilibrium with an internal magnetic field having both toroidal and poloidal components; or a Field Reversed Configuration (FRC), which also has a toroidal magnetic topology, but can be more elongated in the axial direction with an outer surface being similar to a prolate ellipsoid, and which has primarily a poloidal magnetic field, with no toroidal magnetic field component. CT plasmas can be formed in a range of magnetic configurations, including ones that exist in states that are in between spheromak and FRC states. Other configurations of magnetized plasma include tokamaks, reversed field pinches (RFP) and stellarators, all of which use external coils to provide toroidal magnetic field at the wall of a plasma confinement chamber (flux conserving chamber). In contrast, spheromaks and FRCs do not have external coils to provide plasma's toroidal field and the magnetic fields are generated by the currents flowing in the plasma.
Controlled thermonuclear fusion is based on the fusion of light nuclei present in the plasma to form a heavier nucleus. Plasma needs to confine nuclei for a sufficiently long time to allow enough of such nuclei to fuse. Therefore, stabilization and maintaining the plasma in a stable configuration is very important for any fusion system and fusion scheme. In case of magnetized plasma configurations, plasma magnetic field (poloidal and/or toroidal field component) is a key plasma property related to plasma stability and plasma performance.